The age of Homo naledi and associated sediments in the Rising Star Cave, South Africa

Abstract

New ages for flowstone, sediments and fossil bones from the Dinaledi Chamber are presented. We combined optically stimulated luminescence dating of sediments with U-Th and palaeomagnetic analyses of flowstones to establish that all sediments containing Homo naledi fossils can be allocated to a single stratigraphic entity (sub-unit 3b), interpreted to be deposited between 236 ka and 414 ka. This result has been confirmed independently by dating three H. naledi teeth with combined U-series and electron spin resonance (US-ESR) dating. Two dating scenarios for the fossils were tested by varying the assumed levels of 222Rn loss in the encasing sediments: a maximum age scenario provides an average age for the two least altered fossil teeth of 253 +82/–70 ka, whilst a minimum age scenario yields an average age of 200 +70/–61 ka. We consider the maximum age scenario to more closely reflect conditions in the cave, and therefore, the true age of the fossils. By combining the US-ESR maximum age estimate obtained from the teeth, with the U-Th age for the oldest flowstone overlying Homo naledi fossils, we have constrained the depositional age of Homo naledi to a period between 236 ka and 335 ka. These age results demonstrate that a morphologically primitive hominin, Homo naledi, survived into the later parts of the Pleistocene in Africa, and indicate a much younger age for the Homo naledi fossils than have previously been hypothesized based on their morphology.DOI: http://dx.doi.org/10.7554/eLife.24231.001

Palaeodemographics of individuals in Dinaledi Chamber using dental remains

“…However, spatial proximity is not particularly insightful in the Dinaledi Chamber assemblage, in part because of the unusually dense clustering of the remains, and in part because it is evident that some of the deposit has been reworked after the initial deposition of the remains. 2,3 Some parts of the deposit preserve articulated remains, such as parts of a lower limb, hand and foot remains, some thoracic elements and dentition in situ. The majority of elements (94%) were recovered out of articulation, with fragmentary elements from different individuals intermingled with each other.…”

“…27,28 The wide variability in representation of immature remains in the South African caves may reflect the difference in taphonomic processes, as the fossil accumulation in these sites occurred by heterogeneous processes, in contrast to Dinaledi, which may represent a comparatively more limited variability. 3 In particular, it has been argued that the high representation of young male adults at Swartkrans may reflect the effects of social structure and dispersal on predation risk. 29 The A.L.333 Australopithecus afarensis locality at Hadar, Ethiopia, may be more comparable with Dinaledi in representing a limited time horizon, and includes at least 17 individuals -9 adults and a minimum of 8 immature individuals.…”

“…The situation of the fossil assemblage, with hominins attributable to one geological unit, suggests that the remains reached the Dinaledi Chamber over a short geological time span, although several aspects of their taphonomic condition provide evidence that the remains did not enter the chamber in a single instantaneous event. 2 The deposition of the hominin remains occurred between 236 000 and 335 000 years ago 3 -placing them in the later Middle Pleistocene. The degree of morphological variability within this assemblage is very slight; dental and postcranial dimensions are consistent with the variability found within single populations of living humans.…”

“…These aspects include the absence of highly calcified breccia encasing the remains, the absence of non-hominin macrofaunal remains, and the present inaccessibility of the Dinaledi Chamber itself. [2][3][4][5] The Dinaledi assemblage presents an uncommon opportunity to examine a fossil species at the population-level perspective. We have undertaken a preliminary study of the dental remains from this assemblage to assess them as biomarkers of life-history stages of these hominins.…”

Naledi: An example of how natural phenomena can inspire metaphysical assumptions

“…The Naledi remains and the surrounding sediment in Lesedi Chamber have been dated at between 236 000 and 335 000 years by measuring the concentration of radioactive elements (Dirks et al 2017). This date is as controversial as the claim that Naledi buried its dead and generates more questions than answers.…”